1. Field of the Invention
The present invention relates to a recording liquid suitable for use in the ink-jet recording process in which droplets of recording liquid called an ink are flown from a recording head through its orifices to perform recording, and more particularly to a recording liquid giving an ideal black color.
2. Description of the Prior Art
Ink-jet recording generates less noise and permits high speed recording on plain paper without the necessity for any special fixing treatment, so that various types of ink-jet recording systems currently are being investigated vigorously.
The recording liquid used for these ink-jet recording systems needs to fulfill several requirements. For example, its physical properties such as viscosity, surface tension, etc. should be each within a proper range, so that it will not clog a fine spout (orifice); it should form images of bright color tone and of sufficiently high optical density, and it should not undergo a change in physical properties or deposit solid matter, during storage.
In addition, recording by the recording liquid should be accomplished without particular restriction as to the kind of recording medium used, including paper, which is the most typical recording medium; it should exhibit a high rate of fixing on recording media; it should give images excellent in resistances to water, light, and attrition; it should form images with a high degree of resolution; it should be substantially non-corrosive as to any of the components of an ink-recording device it contacts, and it should not easily or readily absorb water vapor from the atmosphere.
Since the recording liquid used for ink-jet recording is composed basically of a coloring component dye and its solvent, the above performance characteristics required are much affected by the inherent properties of the dye. Accordingly, it is very important in the art to select a dye so as to provide the recording liquid with the above performance characteristics.
The solubility of the dye in the liquid medium is particularly important. A high solubility is essential for maintaining a good anti-clogging property and solution stability of the recording liquid.
It is also particularly important when performing black color printing that the black recording liquid has a pure black color tone without a tinge of any other color. Therefore, it is also very important in the art to properly select dyes as coloring components taking the color tone given by a black recording liquid into consideration.
However, almost none of the known recording liquids in black color satisfy the above noted requirements, particularly when ethanol is used as the primary liquid medium, and especially with respect to solubility and providing a true jet-black color. For example, Solvent Black 46 and a blend of Solvent Black 48 and Solvent Brown 52 are dyes currently being used as coloring components in recording liquids in which ethanol is the liquid medium to give a primary black color. However, Solvent Black 46 gives a purple color rather than a jet-black color and is difficult to filter and exhibits poor resolution. Solvent Black 48 needs to be blended with Solvent Brown 52 to give a black color and to produce a recording liquid having adequate filterability and exhibiting acceptable resolution. Thus, there is a continuing need to develop a black recording liquid in which ethanol is the primary liquid medium which meets the above requirements.